You don’t even need an industrial PhD. In Denmark at least, a PhD study is a paid position, essentially just a job that runs 3 years and results in handing in a PhD dissertation. It pays less than what you get in the industry, but very decently, so no need to balance multiple jobs, just focus on your research.

The Industrial PhD pays the same here, so that’s mostly a position you would take if you specifically want to collaborate with a company on some research project, not something you do because of income considerations.